As the school year revs up, Massachusetts Institute of Technology professor Anant Agarwal looks forward to teaching his most popular class. Last semester, Circuits and Electronics welcomed in 154,000 students – 35 times as many as the entire undergraduate enrollment at MIT.

The class kicked off MIT's new push into online learning. It was the inaugural course of edX, a collaboration with Harvard University and the University of California, Berkeley, to offer top-notch education free of charge to anyone with Internet access.

"If you took the online class, the material would be identical" to the on-campus version, says Mr. Agarwal, president of edX and director of MIT's Computer Science and Artificial Intelligence Laboratory. "It was the same level of difficulty. They took the same exams." Students even received grades, just not academic credit.

This fall, edX will offer seven courses ranging from computer science to public health. Agarwal hopes his circuits class will once again attract students ages 16 to 98 and from more than 150 countries – people who may never get the chance to attend or be able to afford a world-class engineering course.

While edX prepares for its first full semester of science-oriented classes, Coursera offers the same model of free education with a longer list of subjects and schools. Coursera founders Daphne Koller and Andrew Ng have pulled in classes on the humanities, design, and science from Stanford University, Princeton University, the University of Pennsylvania, and several other institutions.

So how do you sign up for these classes?

Both online schools run within a Web browser. You sign up and attend classes through their respective websites, edx.org and coursera.org. Registration takes about 60 seconds.

From there, enrolling in any of the courses is a button click away. Each of the four- to 12-week classes comes with an online library of course materials, lectures, quizzes, and a forum to discuss questions with other students. While the programs cut deals with publishers to offer much of the reading material free of charge, students will be responsible for finding and purchasing some textbooks on their own.

For the most part, these online courses revolve around prerecorded videos. Instructors film lectures specifically for these online courses, pulling in digital slides, images, or historical clips as needed.

Each class has suggested prerequisites, but neither program will stop you from pulling off the digital equivalent of sitting in the back of the room and following along. For example, 154,000 people signed up for Circuits and Electronics last semester, but only 7,000 continued to the end and received a passing grade. Agarwal says that ratio doesn't concern him.

"First of all, this was a hard course, an MIT-hard course, and a number of students quickly realized this," he says. "I think many of them thought that they'd learn the background and then take the course again. A number of them thought that they didn't have enough time, so they wanted to finish the course at their own pace." (As it is, the 7,000 students who passed outnumber MIT's engineering undergrads by more than 3 to 1.)

Coursera's Mr. Ng says the online classes can't replace a four-year degree program, but he's already seen the project make a difference in students' lives.

"Anecdotally, we've heard of many students getting jobs or receiving promotions as a direct result of having these courses on their résumé," says Ng, who heads Stanford's Artificial Intelligence Lab. Silicon Valley companies in particular have reached out to the students who received top marks in Coursera's computer science classes, he says.

The participating universities hope to learn from online classes, as well. For the past four years, Ms. Koller, the other Coursera founder, has used online teaching methods in her classes at Stanford. She asks students to watch videos and complete quizzes ahead of normal classes.

That way, "when I walked into class, I would know exactly what parts the students understood and got full marks on in the quizzes, and what issues were more problematic," she says. "I could then focus the class time on clarifying the misconceptions."

Fall courses for edX begin in September and October. New Coursera classes start throughout the year.